from The Century Dictionary and Cyclopedia

n. firework consisting of a small explosive charge and fuse in a heavy paper casing

n. (British informal) pork sausage

Etymologies

bang +‎ -er; the sausages were so called because of the risk of explosion if not carefully cooked, due to excessive amounts of water stored inside the sausages to increase their mass and saleability. (Wiktionary)

Examples

A wall-banger is something that fails spectacularly on all three counts.